The present invention relates to a muffler apparatus and in particular to an improved muffler apparatus having a solid, open-ended tubular structure in the intake or exhaust passageways.
Preventing, decreasing or otherwise mitigating various types of pollution has become increasingly important, particularly in high population areas. One type of pollution which has received increasing attention is high levels of noise which often create high levels of anxiety and annoyance, and may even cause physical harm.
Engines, and in particular, internal combustion engines, constitute a major source of high noise levels. Consequently, various muffler devices have been developed for both the intake and exhaust passageways. While these devices have succeeded in substantially reducing the noise level from engines, it is desired to reduce the noise levels even further. The present invention achieves such a decrease in noise levels by affixing at least one open-ended, non-perforated, tube in the flow path of a conventional muffler arrangement where the flow path is generally defined by a perforated cylinder or tube. In the preferred embodiment of the present invention, the non-perforated or solid tube is concentrically positioned in the interior of the perforated tube.
Several previous patents for muffling devices have incorporated concentric tubular structures. For example, in U.S. Pat. No. 3,503,465 issued on Mar. 31, 1970, to Shunji Kobayashi et al, outer, intermediate and inner hollow truncated cone structures concentrically interconnected with specific divergent angles in the discharge direction are shown. Sound absorbing layers of specific thickness are provided on at least one surface of each cone structure.
More specifically, and with reference, by way of example, to FIG. 5 of that patent, the outer truncated cone member comprises a housing which supports internally thereof a pair of conically shaped diverging tubes. The innermost tube is both perforated and filled with a sound absorbing material. Consequently, it is not opened at both of its ends to provide an unobstructed path through the center of the tube and is not a solid tube as disclosed by the present application. In addition, while the intermediate tube is constructed of solid non-perforated sheet metal, the above-identified patent requires that the intermediate conical tube have a sound-absorbing material affixed on either one or both of its sides. Such sound-absorbing material is not required in the present invention. Furthermore, as described herein, the present invention utilizes a non-conical tube having a constant cross-sectional area along its length. Finally, the solid outer or housing tube also requires that a sound-absorbing layer of material be affixed to its inner surface. As described in the above patent, each of the sound-absorbing layers is held to the corresponding support tube by a perforated layer of sheet metal.
Thus, the above-described patent involves a complex multi-layer structure requiring not only that the inner concentric tubes be conically shaped but further requiring multiple layers of soundabsorbing material. By contrast, the present invention involves a simple tubular structure which is preferably concentrically positioned in the interior of the perforated tube so that the central axis of the solid tube is coincident with the central axis of the perforated tube or cylinder defining the flow path. The structure is surrounded and supported by a solid housing which may be cylindrically shaped or may be conically shaped.
In U.S. Pat. No. 1,968,312 entitled "Air Cleaner and Silencer" issued in 1934 to G. C. Rensink, a muffler device is disclosed comprising an air-intake apparatus adapted to be connected to a carburetor or the like and includes a solid tube which is mounted internally of a perforated tube with the combination being surrounded by a sound-absorbing material and placed within a housing. However, in that patent, the perforated tube is closed at both of its ends requiring that the flow path of gases be lateral to the longitudinal axis of the perforated tube. Consequently, the gas must flow from the outside, laterally through the sound-absorbing material, through the perforations in the perforated tube, and then longitudinally down through the solid tube. By contrast, the flow path of gases in the present invention is always along the longitudinal axis of the perforated tube. Furthermore, the gases are not permitted to flow through the perforations and sound-absorbing material either from or to the outside.
In U.S. Pat. No. 1,995,071 granted to R. J. MacKenzie et al, a silencer device is provided with a sold tube concentrically positioned internally of a perforated tube which is positioned inside a housing. However, the solid tube is not opened at both ends. Consequently, there is no continuous and unobstructed passageway through the solid tube.
In U.S. Pat. No. 4,045,157, issued on Aug. 30, 1977, to Peterson, a silencer device is disclosed having a plurality of axially disposed tubes adapted to be connected to the air intake orifice of an industrial burner. Although the specific structure disclosed includes a solid tube which is disposed axially of a perforated tube used as part of the muffler apparatus, the solid tube is specifically disclosed as being a viewing tube which is normally closed by a member identified by the reference numeral 30 in FIG. 2 of that patent.
Consequently, by contrast to the above-described references, the present invention provides a simple structural modification in a conventional muffler having an unobstructed passageway defined by a perforated tube or other cylindrical structure. This modification comprises a solid tube, opened at both of its ends to provide an unobstructed pathway therethrough, disposed internally of the perforated tube structure so that gases pass not only through the passageway defined by the solid tube but through the passageway defined by the region between the internal surface of the perforated tube and the external surface of the solid tube.
Although the specific physical principles which operate to cause a reduction in noise levels are unknown, tests have demonstrated that the present invention results in a noise level reduction in a Kawasaki 1000 motorcycle of approximately five decibels when compared to the same motorcycle without the present invention. Furthermore, it has been found that when the present invention is used in the exhaust passageway, the pollution content of the exhaust gases is also substantially reduced. Finally, it will be appreciated that several open-ended solid tubes may be utilized and may be positioned in either a cluster or concentric arrangement in accordance with the present invention.